The present invention relates to techniques for monitoring and controlling the manufacture of a moving web of product, such as a web of tissue product. More particularly, the present invention relates to an apparatus and method that provides composition information regarding the moving web which can be used to control the manufacturing process.
Modern facilities for the production of facial tissue and other fibrous webs can operate at line speeds in excess of 2000 feet/minute. As the web progresses through the manufacturing process, various substances are often applied to impart certain desirable characteristics to the final product. For example, tissue product may be impregnated with a relatively xe2x80x9cheavyxe2x80x9d add-on, such as a skin lotion or moisturizer. Other substances, such as analgesics or other over-the-counter medications, may also be applied in some cases.
Information regarding the composition of the web product has been obtained in the past using xe2x80x9coff-linexe2x80x9d analysis. Specifically, a sample of the product has simply been removed from the web and analyzed in a laboratory for its constituent components. For example, a xe2x80x9cmass balancexe2x80x9d analysis has often been used to determine the concentration of lotion applied to facial tissue. According to this technique, the substance in question is removed from the sample by extraction. Weighing the sample both before and after the extraction yields the weight, and thus the concentration, of the lotion.
Compositional information derived by off-line analysis is of little use in making instantaneous adjustments to the manufacturing process. Due to the line speeds at which the web product moves, application of excess quantities of lotion or another such substance can quickly become costly. In addition, a pure mass balance analysis provides no information regarding the concentration of the substance of interest at various locations across the web""s surface. Furthermore, mass balance is often inadequate to determine concentration of xe2x80x9clighterxe2x80x9d add-ons such as medications.
The present invention recognizes and addresses the foregoing disadvantages, and others, of the prior art. Accordingly, it is an object of the present invention to provide reliable information regarding the composition of a moving web on a real-time basis.
It is a further object of the present invention to simultaneously provide composition information in relation to multiple aspects of a moving web for purposes of process control or quality analysis.
It is a more particular object of the present invention to provide a graphical display of composition information regarding the make-up of a moving web.
It is a further object of the present invention to provide various improvements in the manufacture of paper tissue product.
Some of these objects are achieved by a real-time method of deriving composition information regarding a moving web in a manufacturing environment. According to the method, a photodetector assembly is provided having a plurality of photodetectors at respective detection locations across the transverse direction of the moving web. The moving web is then illuminated so as to provide electromagnetic energy at each of the photodetectors. At least two selected frequencies of electromagnetic energy are then measured at each of the detection locations. Finally, the composition information for each detection location is derived based on absorbance of electromagnetic energy thereat.
Exemplary methodology further comprises the step of controlling application of the predetermined component to the moving web based on the derived composition information. For example, application of the predetermined component may be controlled automatically based on the composition information. Alternatively, or in addition, a graphical display can be presented to a human operator showing quantitative levels of the predetermined component in a cross direction of the moving web. In such cases, application of the predetermined component can be manually controlled by the human operator.
Where a graphical display is produced, the graphical display can illustrate quantitative levels correlated to a two- or three-dimensional representation of the moving web. A two- or three-dimensional representation is preferred as it yields a graphical display which takes advantage of the human operator""s natural pattern recognition skills. Preferably, the graphical display will show quantitative levels of the predetermined component in both cross and machine directions.
Other objects of the present invention are achieved by an apparatus for deriving composition information regarding at least one predetermined component of a moving web. The apparatus comprises a plurality of radiation sources adapted to illuminate the web with electromagnetic energy in at least two predetermined frequency bands. The apparatus further includes a photodetector assembly having a plurality of photodetectors spaced apart from the moving web for detecting levels of electromagnetic energy in the respective frequency bands. In addition, electromagnetic energy levels are detected at multiple detection locations across the transverse direction of the moving web. Processor means in electrical communication with the photodetector assembly are also provided. The processor means are operative to derive composition information for each detection location based on absorbance of electromagnetic energy thereat.
In exemplary embodiments, the apparatus may further comprise display means for presenting a graphical display showing quantitative levels of the predetermined component in a cross direction of the moving web. Preferably, the display means may be operative to present the quantitative levels correlated to a two- or three-dimensional representation of the moving web to advantageously utilize the pattern recognition skills of the human operator. The display means may also be configured to further show quantitative levels in a machine direction of the moving web.
In some embodiments, the plurality of radiation sources may be situated on a same side of the moving web as the photodetector assembly. In other embodiments, the plurality of radiation sources may be situated on an opposite side of the moving web from the photodetector assembly. Of course, the radiation sources may be placed on both sides of the moving web in some cases.
Other objects of the present invention are achieved by a real-time method of deriving composition information regarding at least one predetermined component added to a moving web of tissue paper in a manufacturing environment. According to the method, the moving web is illuminated with electromagnetic energy in at least two predetermined frequency bands. Next, electromagnetic energy as diffused by the moving web is measured at each of a plurality of detection locations across a transverse direction thereof. Composition information for each of the detection locations is derived based on absorbance of electromagnetic energy thereat. Finally, application of the predetermined component to the moving web is controlled based on the component information.
Additional objects of the present invention are achieved by a realtime method of deriving composition information regarding at least one predetermined component added to a moving web. One step of the method involves illuminating the moving web with electromagnetic energy. At each of a plurality of detection locations across a transverse direction of the moving web, electromagnetic energy is measured in a plurality of frequency bands falling within a frequency range of 0.2-200 microns. The spectral information from the frequency bands is then combined into a supervector. An additional step involves processing the supervector using multivariate mathematical techniques to produce a spatial data matrix of the composition information as correlated to the detection locations.
Other objects, features and aspects of the present invention are achieved by various combinations and subcombinations of the disclosed elements, which are discussed in greater detail below.